Luftwaffles said:
The whole movie leaves it wide open for a sequel. I want to know whats the deal with David instead. He finds slime on the walls when they first entered the temple and says "impressive" like he knows where it came from. He comments on how "its every childs wish to kill their parents". He was the only one who could read and operate the glyphs inside the temple and ship, he heard the space jockeys conversation in the hypersleep/pilot chamber, hell he even talked to one of them. (we dont even know what he said, it may not be in the interests of Weyland too)
AS for why he infected Holloway in the first place. Remember how David asked Holloway, what would he be willing to do for answers, "everything" maybe he took that as the go ahead to experiment on him. Find out what it does because Weyland commanded him to "Try harder". And on par with Dr Ash in Alien, it was clear that company bots treated the crew as expendable in favour of the companies agenda. Not until Bishop-bot in Aliens were the droids implanted with (what i assume) are the 3 laws of robotics.
If I remember correctly, David was observing the goo between his fingers when he said "Impressive." It was glowing, or seemed to have electricity (or something) flowing through it, especially when distressed. From I gathered, he put two and two together and realized it was some sort of contact liquid that made the stone symbols a touch pad. Sort of a big leap, but, meh, he is an android, after all.
As for the language barrier, if you remember at the beginning of the movie, David is studying ancient human languages trying to find their origin while everyone is in hyper-sleep. As the theory went, if they put us here on Earth, then maybe our early languages are derived from theirs. Once David "learned" the language, it would be basically useless for anyone else to even try.